Method of making formic acid.



ducing formic acid fromformates.

STATES PATENT OFFICE.

WILLIAM H. WALKER, OF BOSTON, MASSACHUSETTS, ASSIGNOR TO MERRIMAG CHEMI-CAL COMPANY, 015 BOSTON, MASSACHUSETTS, A CORPORATION OF MASSACHU-SETTS.

METHOD OF MAKING FORMIC ACID.

1,048,609, Specification of Letters Patent.

No Drawing.

To all whom it may concern.

Be it known that I, WILLIAM H. WALKER, a citizen of the United States,residing at Boston, in the county of Sufl'olk and State ofMassachusetts, have invented certain new and useful Improvements inMethods of Making Formic Acid, of.which the following is aspecification.

The. object of this invention is to provide an eflicient and economicalmethod of pro- In U. S. Letters- Patent, No. 806,660

. granted December 5, 1905, to Max Hamel for a process of makingconcentrated formic acid it is stated On account of the ease with whichformic acid decomposes in the presence of concentrated sulfuric acid thetransformation of the dry formates could only be effected with sulfuricacid having a strength of at most 60 Baum. It is further stated thereinThe mixing of the drytformate with the sulfuric acid cannot for variousreasons be effected so exactly as to obtain a good yield. Thus ifhigh-concentrated sulfuric acid is allowed to drop on formate a veryconsiderable rise of temperature locally occurs which cannot be removedby cooling, as in the mass lumps or the like are. formed, so that themass becomes thick and camiot be stirred, and the sulfuric acid beingnot rapidly combined comes in contact with the formic acid set free anddecomposes the same.

I have discovered that although these statements are correct as appliedto sodium formate in its commercial form which while apparentl drycontains a considerable proportion 0 moisture, probably largely combinedtherewith as a water of crystallization,

they are not correct as applied to the salt from which substantially all.of the water including the water of crystallization has been removed byappropriate dehydrating methods. Sodium formate is'quite deliquescent,and the salt which has been exposed to moist air or which has not'beencarefully dried and thereafter shielded from moisture contains aconsiderable proportion of water, usually from two to three per cent.,from which it parts with difiic'ulty. If sodium formate be dried attemperatures above 100 (3., for a sufficient time, for instance at about130 0., for four or five hours, or atalower I 'is water any substantialloss of acid would Patented Dec. 31, 1912.

Application filed April 11, 1908. Serial No. 426,605.

temperature under reduced pressure or in vacuo, it will contain not morethan 0.4 per cent. of moisture. I have found that this dried orsubstantially water free salt may be employed for the production offormic acid with a high degree of efficiency under conditions which arequite inapplicable to ordinary sodium formate. For example, if sulfllllCacid containing about 88 per cent. of H SO be added to sodium formatesubstantially free from water, under condit ions ermitting good mixinand with reasonab e cooling of the reacting mass, there is practicallyno decomposition ofthe formic acid by the sulfuric acid. Under theseconditions the formic acid produced is found to be formed insubstantially the theoretical proportion and to possesssubstantially'the theoretical concentration, showing that practically nodecomposition has occurred; for since one 'of the products ofdecomposition result in a diluted product. The drying of the salt isalso advantageous as a preliminary to its reaction with sulfuric acid ofeven much higher concentration. .By proceeding as above described thenecessity for providing an additional anhydrous solvent for the salt maybe avoided and the expense of producing formic acid of any desiredconcentration up to the so-called anhydrous state, may be materiallylessened.

While I have described specifically the decomposition of sodium formate,it will be understood that the invention is applicable to thepreparation of formic acid from other formates. The formic acid producedas above described may be recovered by distillation or in any desired orusual manner.

I claim The process of making formic acid which consists in reactingwith strong sulfuric acid 95 upon a formate substantially free fromwater, whereby the reaction proceeds without injurious rise oftemperature or substantial loss of formic acid.

In testimony whereof, I aifix my signa- 100 ture in presence of twowitnesses.

WILLIAM H. WALKER. Witnesses:

WALTER HUMPHREYS, J. M. CoMs'rocK.

